It is funny when they do that although it doesn't do the carpet any good. I expect most of us cat owners have long given up being house proud even if we ever were!
I will put it down to a new habit he has developed I think, and very sweet it is too. It is such a performance, he completely flattens himself to the floor with his chin pushed into carpet and legs all splayed out, if I can catch him on camera or video I will post it to give you a cute overload!
XXX